Gluon saturation effects in relativistic U+U collisions

We examine entropy production in relativistic U + U collisions on the basis of a color glass condensate (CGC) type picture as implemented in the Kharzeev-Levin-Nardi model (KLN). In this framework, we find that the peak entropy density produced in tip-on-tip U + U collisions is about 30% greater than that seen in central Au + Au collisions. Although the resulting difference in the produced charged particle multiplicity between tip-on-tip and side-on-side collisions is smaller than that predicted by previous Glauber model estimates, it is still large enough to allow for experimental discrimination between average orientations of the uranium nuclei. We also point out that in the saturation/CGC approach the collision geometry plays a more important role than previously believed, and that the observed centrality dependence of the produced particle multiplicity per participant in Au + Au collisions can be qualitatively reproduced even without running coupling effects.